The invention relates to a method for operating an internal combustion engine, especially of a motor vehicle, wherein fuel is directly injected into a combustion chamber either in a first operating mode during a compression phase or in a second operating mode during an induction phase. In the method, a switchover is made between the two modes of operation and the operating variables, which influence the outputted torque of the engine, are controlled (open loop and/or closed loop) differently in the two operating modes in dependence upon the demanded torque. Furthermore, the invention relates to an internal combustion engine, especially for a motor vehicle, having an injection valve with which fuel can be injected directly into a combustion chamber either in a first operating mode during a compression phase or in a second operating mode during an induction phase. The engine includes a control apparatus for switching over between the two modes of operation and for different control (open loop and/or closed loop) in the two modes of operation of the operating variables in dependence upon a requested torque. The operating variables influence the outputted torque of the engine.
Systems of this kind for direct injection of fuel into the combustion chamber of an internal combustion engine are generally known. A so-called stratified charge operation as first operating mode and a so-called homogeneous operation as second operating mode are distinguished. The stratified charge operation is used especially for smaller loads; whereas, the homogeneous operation is used for larger loads applied to the engine.
In stratified charge operation, the fuel is injected into the combustion chamber during the compression phase of the engine in such a manner that, at the time point of the ignition, a fuel cloud is located in the direct vicinity of the spark plug. This injection can take place in different ways. Thus, it is possible that the injected fuel cloud is already located at the spark plug during or directly after the injection and is ignited by the spark plug. Likewise, it is possible that the injected fuel cloud is conducted to the spark plug via a charge movement and is only then ignited. In both combustion methods, no uniform fuel distribution is present, instead, a stratified charge is present.
The advantage of the stratified charge operation is that there, with a very small fuel quantity, the applied smaller loads can be taken care of by the engine. Larger loads can, however, not be satisfied with the stratified operation.
In homogeneous operation, which is provided for such larger loads, the fuel is injected during the induction phase of the engine so that a swirling and therefore a distribution of the fuel can still easily take place in the combustion chamber. To this extent, the homogeneous operation corresponds approximately to the operation of internal combustion engines wherein fuel is injected into the intake manifold in the conventional manner. As required, the homogeneous operation can be used also for smaller loads.
In stratified charge operation, the throttle flap in the intake manifold, which leads to the combustion chamber, is opened wide and the combustion is essentially controlled (open loop and/or closed loop) only by the fuel mass to be injected. In homogeneous operation, the throttle flap is opened or closed in dependence upon the requested torque and the fuel mass, which is to be injected, is controlled (open loop and/or closed loop) in dependence upon the inducted air mass.
In both operating modes, that is, in the stratified charge operation and the homogeneous operation, the fuel mass, which is to be injected, is additionally controlled (open loop and/or closed loop) in dependence upon a plurality of additional operating variables with a view to an optimal value with respect to fuel saving, exhaust-gas reduction and the like. The control (open loop and/or closed loop) is then different in the two operating modes.
In the control (open loop and/or closed loop) of direct-injecting internal combustion engines, each of the two operating modes should be considered separately. Likewise, it should be guaranteed that, for the switchover especially from the homogeneous operation into the stratified charge operation, the torque, which is outputted by the engine, remains constant.
It is an object of the invention to provide a method for operating an internal combustion engine which makes possible a switchover from the second into the first mode of operation which is constant as to torque.
This object is solved with a method in accordance with the invention and/or with an internal combustion engine in accordance with the invention in that the fuel mass which is to be injected in the first operating mode is determined or can be determined in dependence upon the parameters of the engine which form the basis of the injections of the second mode of operation.
With the use of operating variables of the homogeneous operation with the control (open loop and/or closed loop) of the stratified charge operation, the possibility is provided that, when switching over from the homogeneous operation into the stratified charge operation, a switchover jolt because of the torque differences can be avoided. In this way, the smooth running of the engine and the comfort for the driver of the motor vehicle is increased.
Furthermore, the control (open loop and/or closed loop) of the stratified charge operation takes place on the basis of the control (open loop and/or closed loop) of the homogeneous operation. From this, the advantage is provided that the control (open loop and/or closed loop) of the homogeneous operation, especially the software modules or the like required therefor, can be taken over from known internal combustion engines which are operated only in homogeneous operation. In this way, it is only necessary to set the control (open loop and/or closed loop) for the new additional stratified charge operation. This control (open loop and/or closed loop) is then xe2x80x9csuperposedxe2x80x9d on the known software modules so that, in total, a control (open loop and/or closed loop) is provided for a direct-injecting engine.
In an advantageous embodiment of the invention, the fuel mass, which is to be injected in the first mode of operation, is determined in dependence upon a lambda control factor of the second operating mode. This is one of several possibilities with which a constant torque can be achieved when switching over from the homogeneous operation into the stratified charge operation.
It is especially advantageous when the lambda control factor is changed by means of a time-dependent and/or rpm-dependent characteristic line.
In a further advantageous embodiment of the invention, the lambda control factor of the second mode of operation is stored. This defines a measure which makes possible a torque-constant switchover from the stratified charge operation back into the homogeneous operation.
In a further advantageous embodiment of the invention, the fuel mass, which is to be injected in the first mode of operation, is determined in dependence upon an intake air temperature and/or an ambient pressure. In this way, the switchover from the homogeneous operation into the stratified charge operation can be further improved in the sense of a constant torque.
In an advantageous embodiment of the invention, the fuel mass, which is to be injected in the first operating mode, is determined in dependence upon the requested torque. Here, it is especially advantageous when the requested torque is changed by means of an rpm-dependent characteristic line and/or when the requested torque is changed in dependence upon a specific thermal value of the fuel and/or an efficiency of the combustion of the engine in the first operating mode.
The realization of the method of the invention in the form of a control element is of special significance. The control element is provided for a control apparatus of the engine, especially of a motor vehicle. A program is stored on the control element which can be run on a control apparatus, especially on a microprocessor, and is suitable for carrying out the method of the invention. In this case, the invention is therefore realized by a program which is stored on the control element so that this control element, which is provided with the program, defines the invention in the same way as the method for whose execution the program is suitable. As a control element, especially an electric storage medium can be used, such as a read-only-memory.
Further features, application possibilities and advantages of the invention become evident from the description of the embodiments of the invention which follows and which are shown in the drawing. All features, which are described or illustrated, are, for themselves or in any desired combination, the subject matter of the invention independently of their composition in the patent claims or their dependency as well as independent of their formulation or illustration in the description or in the drawing.